Farm Talk

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October 22, 2013

Approaching disease from different perspectives

Parsons, Kansas — What does a California field of barley from 1951 have to do with a field of Kansas wheat in 2013? The much reviled disease barley yellow dwarf (BYD) virus was named from a ferocious outbreak of the disease back in 1951 in California. The story goes that some fields of the cereal grain turned a bright yellow within a single week in April. By the end of May, symptoms of the disease were found in every barley producing county across the state.

As stated earlier, BYD is caused by a virus. This virus infects a broad range of plants including cereal grains, perennial weeds, and forage grasses. Viral diseases, in general, need a vector to carry them from plant to plant. In BYD’s case, the virus is vectored by aphids. In Kansas, the two most important vectors are greenbugs and bird cherry-oat aphids. The virus is transmitted into the plant through the aphid’s saliva.

The aphids migrate into Kansas from southern states in the fall through the spring. Once the aphid feeds on an infected plant it then becomes a carrier of the virus. The virus has no known effect on the aphids themselves. Also, direct damage from the feeding is rarely enough to cause an issue.

Two K-State researchers have recently published information concerning BYD. C. Michael Smith, K-State Entomology Professor, has been studying the aphids and William Bockus, K-State Plant Pathology Professor, has been comparing disease levels to yield loss.

In Dr. Smith’s study which started in 2012, the researchers looked at what percentage of aphids collected actually carried the BYD virus. To begin the study, they first had to develop a technique sensitive enough to detect the virus in aphids. Then they had to decided how to accurately sample the aphids since the virus is unable to be detected in dead aphids. To do this, they needed the cooperation of some county Extension agents, area agronomy specialists, consultants, and producers.

The first results have been released, and the numbers are interesting, at least to me. From southeast Kansas, there were five samples submitted, three from Wilson County, and one each from Crawford and Cherokee Counties. The three samples from Wilson county resulted in 10 percent, 20 percent, and 20 percent of the aphids in each sample carrying the BYD virus. The sample from Cherokee County included 30 percent of the aphids carrying the BYD virus. Unfortunately for the producers in Crawford County, 100 percent of the aphids in the sample submitted carried the BYD virus. Only one other sample in the state (from Butler County) reached this level.

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